A conventional vibrating gyroscope is illustrated in FIG. 11. In this vibrating gyroscope, piezo-electric elements 2 and 3 of vibrator 4 are respectively connected via the respective impedance elements Z1 and Z2 to the output side of drive apparatus 6. The output side of this drive apparatus 6 is also connected, via still another impedance element Z3, to capacitor C. Drive signals from drive apparatus 6 are simultaneously applied to the piezo-electric elements 2 and 3 and on capacitor C.
The outputs at the respective nodes of impedance elements Z1 and Z2 and piezo-electric elements 2 and 3 are combined. The combined output and the output at the node of impedance element Z3 and capacitor C are supplied to differential amplifier 7. The differential output from differential amplifier 7 is fed back to drive apparatus 6, so that vibrator 4 is self-vibrating. The outputs at the respective nodes of impedance elements Z1 and Z2 and piezo-electric elements 2 and 3 are supplied to another differential amplifier 8, so as to obtain an angular velocity to detection signal based on the output from differential amplifier 8.
An example of the vibrator 4, shown in FIG. 12, has a square cross-sectional shape and has piezo-electric element 2 on one side surface 1a of vibration member 1 having a resonance point and piezo-electric element 3 on another side surface 1b adjoining side surface 1a. Another example of a vibrator, shown in FIG. 13 has piezo-electric elements 2 and 3 split in the wide direction on the same side of vibration member 1. Another example of a vibrator, shown in FIG. 14, has piezo-electric elements 2 and 3 on opposite sides of vibration member 1. Another example of a vibrator, shown in FIG. 15, has the respective piezo-electric elements 2a and 2b on opposite side surfaces of vibration member 1 and connects them in parallel so that they act essentially as one piezo-electric element 2, while also having the respective piezo-electric elements 3a and 3b on the other opposite sides so as to connect them in parallel so that they act essentially as one piezo-electric element 3.
Still another example of vibrator 4, shown in FIG. 16, has a triangular cross-sectional shape and has piezo-electric elements 2 and 3 on two side surfaces of vibration member 1 having a resonance point. Another example of a vibrator 4, shown in FIG. 17, has a circular cross-sectional shape and has piezo-electric elements 2 and 3 on the peripheral surface of vibrator member 1 having a resonance point. Thus, members having essentially two piezo-electric elements are formed on the side surfaces of vibration members having various sectional shapes. Further, a vibrator 4 made up of at least two piezo-electric elements 2 and 3 in vibration member 1, as illustrated in FIG. 12 to FIG. 17, is equivalently represented as shown in FIG. 18.
However, the conventional vibration gyroscope shown in FIG. 11 applies the drive signals from drive apparatus 6 onto piezo-electric elements 2 and 3 via impedance elements Z1 and Z2. This causes the signal level applied to piezo-electric elements 2 and 3 to drop when the impedances of piezo-electric elements 2 and 3 drop in the vicinity of the mechanical series resonance frequency f.sub.s in vibrator 4. The frequency at which the output from differential amplifier 7 is at a maximum and the mechanical series resonance frequency f.sub.s do not coincide. This phenomenon will be explained next, with reference to FIG. 19 and FIG. 20.
FIGS. 19A and B illustrate examples of measurements of the frequency and phase characteristics of admittance .vertline.Y.vertline. of vibrator 4 as shown in FIG. 12. FIGS. 20 A and B show the transfer and phase characteristics of differential amplifier 7. The vibration gyroscope illustrated in FIG. 11 connects piezo-electric elements 2 and 3 directly to the respective impedances Z1 and Z2, so that, as will be understood from FIG. 19A, the signal levels applied to these piezo-electric elements 2 and 3 decrease in the vicinity of the mechanical series resonance frequency f.sub.s where .vertline.Y.vertline. is large and increase in the vicinity of the mechanical parallel resonance frequency f.sub.s where .vertline.Y.vertline. is small. Therefore, the output of differential amplifier 7 receives the effect of the mechanical parallel resonance frequency f.sub.a with its high signal level. Therefore, the maximum value frequency, as shown in FIG. 20A, shifts to the mechanical parallel-resonance frequency f.sub.a.
As the equivalent circuit in FIG. 21 indicates, vibrator 4 is shown with one piezo-electric element as a parallel resonance circuit where damping capacity Cd is connected in parallel to the series resonance circuit comprising inductor L1, capacitor C1 and resistance R1. Resistances and capacitors, for example, are used for impedance elements Z1 and Z2. When resistances are used as impedance elements Z1 and Z2, the applied signals also create phase changes determined by the value of damping capacity Cd relative to the resistance values of impedance elements Z1 and Z2. Therefore, the levels and phases of the applied signals vary in a complex fashion along with impedance changes in vibrator 4. The frequency where the output of differential amplifier 7 is at a maximum goes to the mechanical parallel resonance frequency f.sub.a.
Furthermore, the equivalent constants of vibrator 4, i.e., damping capacity Cd, inductor L1, capacitor C1 and resistance R.sub.1, have individual temperature dependencies, so that the frequencies where the output of differential amplifier 7 is at a maximum will vary under changes in ambient temperature. Since self-induced vibration occurs at frequencies where the output of differential amplifier 7 is at a maximum, variations in set frequencies of self-induced vibration are easily brought about by changes in ambient temperature.
The mechanical quality coefficient Q.sub.m of vibrator 4 is such that there will be no accurate agreement between the values on the piezo-electric element 2 side and the values on the piezo-electric element 3 side, so that variations in the set frequencies of self-induced vibration cause differences in the outputs of impedance elements Z1 and Z2 and the nodes of piezo-electric elements 2 and 3, so that low voltages and variations tend to occur.
Vibrator 4 has impedance elements Z1 and Z2 connected to piezo-electric elements 2 and 3 which leads to overall high impedance, so that the effects of electrical noise tend to occur at the respective nodes of piezo-electric elements 2 and 3 and impedance elements Z1 and Z2.
Furthermore, in order to cause the vibrator to oscillate at or near its resonance frequency, i.e., self-induced vibration, the prior vibration gyroscope shown in FIG. 11 combines the outputs at the respective nodes of impedance elements Z1 and Z2 and piezo-electric elements 2 and 3. It also supplies this combined out put and the outputs at the nodes of impedance element Z3 and capacitor C to the differential amplifier 7. This leads to the problematic necessity of a large number of parts and high costs, as well as to complicating the circuit structure and hindering miniaturization.